LA PAZ, Jan 30 (Reuters) - Flooding and torrential rains have killed 40 people in Bolivia since November, wrecking highways, crops and thousands of homes in the impoverished country, officials said on Wednesday.

Nearly 400,000 people living in the Andean city of La Paz have been forced to ration their drinking water after mudslides damaged water pipes last week, and the mayor said the shortages could last until March.

State television showed people wading in chest-high water in towns in the central province of Cochabamba, where local media said three young sisters had drowned.

In eastern Santa Cruz province, the head of the local chamber of commerce said the damage to soybean crops and highways was estimated at between $200 million and $500 million, local newspapers reported.

The flooding is blamed on the La Nina weather phenomenon in the Pacific Ocean, which has exacerbated Bolivia's rainy season. The local meteorological service forecast that rains will continue for at least another month.

The situation has worsened this week, and 10 people were killed in the past five days. That brought the death toll to 40 since the heavy rains began two months ago.

President Evo Morales has asked for aid from neighboring countries to meet the food and medical needs of the more than 32,000 families affected by the flooding. Brazil and Chile have sent helicopters to help in rescue efforts.

Government spokesman Alex Contreras said Morales had sent all his cabinet ministers to assess flood damage and help victims in different parts of the country, which is the poorest in South America.